Early bicycles had pedal cranks directly mounted to the front wheel. The mechanical advantage the rider had was established by the ratio of the crank diameter to the wheel diameter, resulting in the production of bicycles with dangerously large wheels to achieve high speeds. However, in the simplest case braking was ever so simple, as the rider could just reverse the direction of pedal force.
The innovation of the chain drive enabled the wheels to be made much smaller and safer by decoupling mechanical advantage from rider altitude. By the early part of this century, mass-produced, chain-driven one-speed bicycles dominated all other styles. Brakes were housed in the rear wheel hub and actuated upon reverse-pedalling.
The next drive train advance was the three-speed bicycle. A thumb-operated shift lever typically shifted the gears in the rear hub-mounted gear box, overcoming the severe speed and climb limits inherent in one-speeders. Braking could still be incorporated into the rear hub and actuated by backpedalling. The "three-speed" represented the last word in production line bicycles for a few years, until the "ten speed", with its multiple-gear-sprocket derailleur, came on the scene.
The so-called "ten speed", with its two front and five rear gear rings, has become generic to multi-gear derailleur-type street bicycles, regardless of the number of "speeds" available. Once the multiple-gear sprocket hurdle had been passed, the number of commonly offered gear ratios proliferated into the 20's.
By the time of the advent of the multi-speed derailleur bicycles, chain drive had become universal. Single-speed bicycles had a chain that was an unvarying, set length, which need not change throughout the operation of the bicycle. This was also true of the three-speed, which used a shift mechanism which did not involve jumping the chain from ring-to-ring. Since both the upper and lower chain runs of the chain loop were always reasonably taut, braking could be accomplished through backpedalling, coupling the backpedalling action to a mechanism internal to the rear wheel hub.
The derailleur system, on the other hand, requires that the chain vary in effective length. This was accommodated by incorporating a spring-loaded idler sprocket in the lower chain run, with the forward-motion tension being applied through the upper run. The idler in a typical multi-speed bicycle can take up to about twelve inches of chain slack.
The old single-speed bicycle brake could be actuated by backpedalling, as minimal slack in the lower chain run made for good braking repose time. With the advent of the derailleur however and the idler pulley with its accompanying twelve inches of chain slack, brakes could no longer be applied by reversing chain direction, practically speaking. By the time the ten to twelve inches of slack had been taken out of the lower chain run, a bicyclist could have plowed into the side of a truck. Hand brakes were thus used and touted as an advance in bicycle brakes, which no doubt they were, since braking force is applied to both wheels instead of just one, and to the periphery of the wheel rather than the hub.
It is inherent in the handbrake system that at least one, and more likely both, of the hands must be maintained in brake-ready position, which is often uncomfortable and awkward. For this reason there are those who think of the reverse-pedal bicycle brake with nostalgia. Of course, the best of both worlds would be to have both hand brakes and foot brakes available, permitting riding in a wider variety of postures, eliminating the necessity of maintaining oneself in the awkward, crouched-over position, while maintaining maximum stopping power. A bi-modal bicycle braking system to accomplish this would be welcomed in the bicycle community.